It is known that thyristors of thyristor-pulse converters can be controlled by applying time-constant and time-shifted trains of control pulses to the switching thyristors and main thyristors of each phase of a thyristor-pulse converter for changing the duration of the conductive state of the main thyristors. In order to reduce power current fluctuations in the power supply and load in the case of polyphase converters, it is necessary that, simultaneously with the generation of time-shifted and time-constant pulse trains, the beginning of operation of each successive phase of the thyristor-pulse converter is shifted with respect to a preceding phase by (1/m)T, where m is the number of phases of the converter and T is the switching period of the thyristors.
Known in the art is a method of digital control of thyristors of m-phase thyristor-pulse converters (cf. "Impulsyne preobrazovately postoyannogo toka" ("D-C Pulse Converters"), "Energia" Publishers, Moscow, 1974), in which the duration t of the conductive state of the thyristors of each phase is changed within the entire control range by sending time-shifted and time-constant pulse trains from each control channel to the corresponding phase of the m-phase thyristor-pulse converter with simultaneous shift of the beginning of operation of each phase by (1/m)T.
The control range .PHI. here and below means the time period during which is controlled the duration t of the conductive state of the thyristors or duty factor .gamma., which is equal to the ratio of the duration t of the conductive state of the thyristor (i.e. the pulse length) to the switching period T EQU .gamma.=t/T
The maximum control range is equal to 0.ltoreq..PHI..ltoreq.T. The time-shifted and time-constant pulse trains are formed by changing the state of the flip-flops of each control channel. In this case, each control channel changes the duration t of the conductive state of the thyristors of one phase within the entire control range, thus repeating the process of shaping a pulse of the same length by each control channel with a time shift of (1/m)T. Each control channel provides control of the pulse duration t in the control zone .phi., which is the time during the pulse duration is controlled by one channel. In the known method, the control zone .phi. of each control channel is equal to the control range .PHI.. In this method of control, it is necessary to provide for all combinations of states of the flip-flops in each channel.
One of the known devices for digital control of thyristors of m-phase thyristor-pulse d-c converters for carrying out the present method (cf. USSR Inventor's Certificate No. 424,290, 1971) includes a master oscillator connected to the input of a clock pulse count unit comprising "m" clock counters. The logic outputs of the clock pulse counting unit are connected to the logic inputs of each of "m" decoders of shifted pulse trains whose data inputs are connected to the data outputs of a switching unit. The switching unit includes "m" bidirectional counters, while its control inputs are connected to the control outputs of the control unit. A combination of a clock pulse counter, a decoder and bidirectional counter forms a control channel.
In the known device, the decoders, clock and bidirectional counters of each control channel must provide a train of pulses within the entire control range, i.e., to provide all combinations of states of the elements and circuits, which results in a high amount of elements of the decoders, clock and bidirectional counters and, therefore, reduces the reliability and efficiency of the control device, increases the consumed power and overall dimensions thereof.